This invention relates generally to a substrate transfer system for transferring a workpiece such as a silicon (Si) wafer, a glass rectangular substrate for a photomask, a glass rectangular substrate for liquid crystal.
A substrate transfer system employing a conventional robot hand for transferring said workpiece is shown in FIG. 6. The substrate transfer system comprises a base 1 in which a driving source is built in, and a robot hand 2 that is mounted on said base 1. The robot hand 2 has a 3-link structure that is provided with a first arm 3, a second arm 4, a third arm 5 and an end effector 6 for supporting a workpiece W. This kind of the substrate transfer system is, as shown in U.S. Pat. No. 5,064,340, uniquely structured such that lengths of first, second and third arms maintain a ratio of 1:2:1 respectively (a=c, b=2a).
Further, as shown in FIG. 7, when an end effector part 7 including the workpiece W moves in a straight line, a middle point 14 that divides the second arm 4 into halves in a longitudinal direction, moves so as to lie in a line between a rotational axis 15 of the end effector 6 and a rotational axis 13 of the first arm 3. Besides, in order for the end effector part 7 including the workpiece W to move in a straight line, rotational speed of arms and end effector is controlled so as to maintain a ratio of 1:2:2:1. Rotational tracks around the rotational axis 13 as a center and a linear state of the arms are indicated by phantom lines in the figure.
In recent years, in order to enhance productivity, the need for reducing an installation area has increased for a substrate processing equipment in which a substrate transfer system is equipped. Therefore, an area for the substrate transfer system is also limited in the substrate processing equipment. Thus, there has been an important object that the substrate transfer system achieves required functions in a minimum installation area.
However, the installation area of the substrate transfer system having a robot hand of a 3-link structure is determined by a minimum rotational radius of arm rotation. The conventional substrate transfer system is, as shown in FIG. 7, uniquely structured such that lengths of the first, second and third arms 3, 4 and 5 maintain a ratio of 1:2:1 respectively, so that the minimum rotational radius of arm rotation can theoretically be calculated by following equations with respect to a rotational angle xcex8 (xcex8 is an angle between the first arm direction and a substrate transferring direction) of the first arm 3 when the robot hand is contracted.
In order to give a straight line motion to the end effector part including a workpiece, it is assumed that the rotational speed of each of the arms and end effector is controlled to maintain a ratio of 1:2:2:1, so that the first arm 3 and third arm 5 always keeps a parallel state regardless of the rotational angle xcex8 of the first arm 3. The rotational radius takes either one of rotational track radiuses (R1, R2 and R3) with respect to the area of the rotational angle xcex8 of the first arm 3 when the robot hand is contracted. R1 is the rotational track radius of the distal end portion of the second arm 4 around the rotational axis of the first arm 3 as a center. R2 is the rotational track radius of the distal end portion of the third arm 5 around the rotational axis of the first arm 3 as a center. R3 is the rotational track radius of the distal end portion of the workpiece W around the rotational axis of the first arm 3 as a center. Each of the rotational track radiuses (hereinafter referred to as rotational radius) is determined based on FIG. 7 by the following equations:
R1=w/2+axc2x7sin xcex8/sin {tanxe2x88x921(tan xcex8/3)}
R2=4axc2x7cos xcex8+w/2
R3=e+d/2xe2x88x924axc2x7cos xcex8
Here, conditions are assumed as follows:
a: length of the first arm
b: length of the second arm (=2a)
c: length of the third arm (=a)
e: length of the end effector (const.)
w: width of the arm (const.)
d: diameter of the circular thin workpiece (const.)
The above equation is obtained in a method below when a segment length of a side OA is assumed to be x in a hatched triangle of FIGS. 8(a) and 8(b) showing details of segments of FIG. 7:
xxc2x7sin xcfx86=b/2xc2x7sin xcex8
x=b/2xc2x7sin xcex8/sin xcfx86=axc2x7sin xcex8/sin xcfx86
Here,
{overscore (QO)}={overscore (BQ)}=2axc2x7cos xcex8
{overscore (PQ)}=axc2x7cos xcex8
∴{overscore (PO)}={overscore (PQ)}+{overscore (QO)}=3axc2x7cos xcex8
And,
{overscore (AP)}=b/2xc2x7sin xcex8=axc2x7sin xcex8
In xcex94APO,
tan xcfx86={overscore (AP)}/{overscore (PO)}=axc2x7sin xcex8/3axc2x7cos xcex8
∴xcfx86=tanxe2x88x921(tan xcex8/3)
Substituting this value into the above equation about x,
x=axc2x7sin xcex8/sin {tanxe2x88x921(tan xcex8/3)}
Here, R1=w/2+x
The maximum value among R1, R2 and R3 that is determined by the above equation becomes the rotational radius R in a time for rotation of the first arm 3 when the robot hand is contracted. The rotational radius R is determined by the following equation:
R=MAX (R1(xcex8), R2(xcex8), R3(xcex8))
The minimum value Rmin in the above equation is the minimum rotational radius that is to be obtained.
For instance, in a conventional example shown in FIG. 9 (equal to FIG. 7, dimensions are described), the rotational radius R in each of xcex8 is indicated as shown in a graph of FIG. 10 (horizontal axis: rotational angle of the first arm 3, vertical axis: rotational radius). At the time, the minimum value Rmin=249.696 mm (xcex8=72.946 deg) of a curve R is the minimum rotational radius in the conventional example shown in FIG. 9.
As described above, in the conventional example in which the ratio between the first, second and third arm lengths is 1:2:1, it is theoretically impossible that the rotational radius takes on a smaller value than the above minimum value Rmin.
This invention is made to solve the above-mentioned problems. One object of the present invention is to provide a substrate transfer system which allows a rotational radius of arms to be smaller than that of a conventional system, and achieves longer transfer distance in an installation area equal to a conventional installation area, thereby making it possible to contribute toward reduction of the installation area of a substrate processing equipment.
In order to achieve the above-mentioned objects, according to one aspect of the present invention, a substrate transfer system transfers a workpiece such as a silicon wafer, a glass rectangular substrate for a photomask, a glass rectangular substrate for liquid crystal with employing a robot hand: wherein said robot hand comprises a link structure including a first arm which is rotatably supported by a base, a second arm which is rotatably supported by a distal end portion of said first arm, a third arm which is rotatably supported by a distal end portion of said second arm, and an end effector for supporting the workpiece, which is rotatably supported by a distal end portion of said third arm; and wherein each of the arms are composed such that a sum length of the first arm and third arm becomes equal to a length of the second arm, and a length of the first arm becomes longer than a length of the third arm.
The above-mentioned composition allows the arm rotational radius to be smaller than a rotational radius of a conventional system, and makes it possible to achieve a longer transfer distance in an equal installation area, thereby contributing toward reduction of an installation area of a substrate processing equipment.
According to another aspect of the present invention, a substrate transfer system transfers a workpiece such as a silicon wafer, a glass rectangular substrate for a photomask, a glass rectangular substrate for liquid crystal with employing a robot hand: wherein said robot hand comprises a link structure including a first arm which is rotatably supported by a base, a second arm which is rotatably supported by a distal end portion of said first arm, a third arm which is rotatably supported by a distal end portion of said second arm, and an end effector for supporting the workpiece, which is rotatably supported by a distal end portion of said third arm; wherein a ratio between each of arm lengths is determined such that a distal end portion of the first arm, a distal end portion of the second arm, a distal end portion of the third arm, and a distal end portion of the workpiece held by the end effector is inscribed in a track circle around a rotational axis of the first arm as a center; and wherein the ratio between each of arm lengths is approximately 1:({square root over ( )}5+1)/2({square root over ( )}5xe2x88x921)/2(≈1:1.618:0.618).
According to further aspect of the present invention, a substrate transfer system transfers a workpiece such as a silicon wafer, a glass rectangular substrate for a photomask, a glass rectangular substrate for liquid crystal with employing a robot hand: wherein said robot hand comprises a link structure including a first arm which is rotatably supported by a base, a second arm which is rotatably supported by a distal end portion of said first arm, a third arm which is rotatably supported by a distal end portion of said second arm, and an end effector for supporting the workpiece, which is rotatably supported by a distal end portion of said third arm; wherein a ratio between each of arm lengths is determined such that a distal end portion of the first arm, a distal end portion of the second arm, a distal end portion of the third arm, and a distal end portion of the workpiece held by the end effector is inscribed in a track circle around a rotational axis of the first arm as a center; and wherein the ratio between each of arm lengths is approximately determined such that a longer portion of the divided second arm length according to xe2x80x9cgolden sectionxe2x80x9d becomes the first arm length, and a lesser portion of it becomes the third arm length.
In the above-mentioned composition, a theoretical minimum value of the minimum rotational radius can be provided. Especially, this composition makes it possible to provide a theoretical minimum value of the minimum rotational radius in the substrate transfer system wherein each of arm lengths is structured such that the sum of the first and third arm lengths equals the second arm length, and the first arm length becomes longer than the third arm length.